Process for cleaning granular materials



y 9, 1963 F. R. OFNER PROCESS FOR CLEANING GRANULAR MATERIALS Filed May 26, 1958 INVENTOR FRANK R. OFNER BY% aA ZMZW ATTORNEY United States Patent "ice m 1 Patented July 9, 1963 1 Frank R. Ofner, Portland, Greg, assignor to Industrial 1 l 2 P ject of the invention is that of providing a process and ap- 3,997,159 paratus for washing wheat, other grains and the like, PROCESS FOR CLEANING GRANULAR which will optimize in a single washing stage the advan- MATEREALS tages now gained in multiple washing stages, and wherein Powertronix, Inc., Portland, Greg, a corporation of the lsylstem compact with the result that it gregon occupies an ins gnificant amount of space compared to Ffled May 26 1953SBLN0737366 the space reqmrement of prior systems (for example, 3 Claims. (ill. 209-2) a space of about 5 x 12' as opposed to several floors of equipment for washers having a capacity of about 330 This invention relates to a process and apparatus for bushels per hour). cleaning granular materials, and more particularly to such Still another object is that of providing a system of the a process and apparatus for washing grains such as wheat. character described, wherein the apparatus because of Many granular materials much be cleaned as a step its structural simplicity and the minimization of relatively in the processing thereof, and this is especially true of moving components, requires but a small initial investgrain. For example, it was early discovered that a num- 15 ment, has a low maintenance cost and has a low power ber of advantages accrued from washing wheat prior to demand. Moreover, the installation expenses are low and converting the same into flour. Among such advantages the equipment can be installed quite rapidly and, if deare the removal of smut and dirt, loosening of the outer sire an integral y beeswing, an improvement in the general sanitary condi- Yet another object is in the provision of an improved tion of the grain, and the production of a more uniform Washing process for wheat and the like and for apparatus flour having :a low ash content, improved color, better to carry forth the same, that materially decreases the milling qualities and an increase in the patent flour prodamage to the grain that is inherent in the scouring action duced. In view of these advantages, it is quite common provided by present washers, but which at the same time today for millers to wash wheat before grinding the same affords a much better and more thorough cleaning of the into flour. grain whereby the product yield is greater. A further Essentially, a single type of washer is in use, and it comobject is to provide 8. Wash g n y g System may ri a large horizontally di d cylinder, Wh t and be noted that the term washer as used in the trade comwater are fed to a closed section of the cylinder where Pfehends y g Stage, Consequently the concepts the washing action takes place. A revolving spiral ribbon of washing and drying per se are not necessarily distinwithin the cylinder carries the wheat after washing through g the ehehaetef desefihed, wherein a much a perforated section thereof, wherein the wheat is rinsed. r Control Of the moisture Content of the end P is The rinsing action is accomplished and controlled through attained-so much better in fact that the control may be manual or mechanically operated valves that determine o s dercd substantially absolute. the quantity of water delivered to the cylinder. There- Yet further Object is in the Provision of Y in after, the spiral ribbon continues to advance the rinsed which the wash water is used to its capacity whereby a grain to a further section of the cylinder wherein a constant much more thorou Washing 0f the g ar ma erial i flew of ir, actuated by the movement of the ribbon, reattained per unit of wash water, with the result that the moves portions of the surface moisture and, in conjuneover-all consumption of wash water is diminished. Addition with the centrifugal force developed which drives ofi tional objects and advantages of the invention will become additional water, partially drys the grain. In addition, a apparent as the specification develops. constant air flow is circulated through the grain and con- An embodiment of the invention is illustrated diagramtinues the drying action until the wheat is discharged. metieelly in the Single View which comprises the drawing Although it is common to wash grain and oftentimes hereof. essential because of the sanitation controls imposed by the The process and apparatus illustrated in the drawing Federal Food and Drug Administration, a number of discomprise three stages that, for identification, may be desigadvantages are attendant with the washing process. Such nated as mixing, washing, and separating and drying. The disadvantages include an excessive increase in the moisture drawing is Provided With legends p ing to t content f the grain; the difiiculty of obtaining an adequate nomenclature and indicating the structural components water supply, which must comprehend three to five gallons omprising parts thereof. of water per bushel of grain; the additional power cost of The first stage comprises a mixer 10- of inverted, frustooperating the washer :appara us; and th dditi l majnconical configuration having a conduit 11 feeding into the tenance requirement cannot be overlooked as an economic hollow interior adjacent the upper end thereof, and which factor. Other disadvantages which have existed heretois adapted to supply liquid or wash water thereto. Also fore but which have been overcome in the manner discommunicating with the interior of the mixer 10' is a conclosed in my patents, Nos. 2,835,984 and 2,835,985, are duit 12 through which granular material such as wheat or th l f grain n-i d fi b the wa h water, the di other grain is fed thereto. The conduit 12 may comprise posal of the wastes, and the high water costs resulting a portion of a screw conveyor, and if so will have a feed from the inability to reuse the wash water. screw 13 cooperatively arranged therewith. It will be Other negative aspects of the general cleaning process noted that both of the conduits 11 and 12 have elongated (water washing being one step thereof) are evidenced openings that communicate with the mix'er 10 along an in the high initial cost of the equipment employed and the arc of the surface thereof whereby the infeed of the ma- Vast amount of space required, which may encompas terials, and particularly the wash water, results in a swirlseveral floors in a mill and incorporate as many as sevening motion thereof wherein the material tends to move teen separate cleaning steps. Additionally, the w he through convolutions following the surface contour of are difficult to operate and, as a consequence, are often the mixer. This results in a thorough and intimate mixing improperly used so that the grain is not adequately cleaned, of the liquid and solids. d even wopse acquires la, gummy coating thereon. The lower end of the mixer 10 is provided with an out- In view of the desirability and frequent necessity of let communicating with a pipe or conduit 14 that diswashing grain, an object of the present invention is to charges into the casing 15 of a pump denoted in general provide a process and apparatus for accomplishing the with the numeral 16. The pump is preferably of a large same which will overcome a number of the important disadvantages inherent in the prior art systems. Another obvolume, low head type; and in the form shown, has multiple stages indicated with the numerals 17, 18;, and 19,

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forced through the stages 13 and 19, and into an outlet pipe or conduit 23. The impellers are respectively mounted upon shafts 24, 25 and 26, rotatably driven by a motor 27 through a gear assembly 28. Ordinarily, the,

impeller 21 and its shaft 25 will be rotated reversely with respect to the impellers 20 and 22 and the shafts thereof.

Preferably, the interior surfaces of the pump casing and the surfaces of the impellers therein will be coated with a resilient material such as rubber to minimize abrasion of the grain. The function of the pump is to further mix the liquid and solids, and to deliver the material to the conduit 23 with a sufiicient pressurehead so that it rises upwardly through the vertically disposed washer 29".

The washer 29 constitutes a tank or cylinder having a plurality of paddles or agitators mounted therein for rotation, and which are driven by a motor 30 through appropriate gearing denoted with the numeral 31. In the form. shown, there are five paddles 32 through 36 which are vertically oriented and extend substantially from top to bottom of the mixer tank 29. At the upper end of the washer 29 is an outlet communicating with a delivery conduit 37. It will be noted that the interconnection of the outlet and delivery conduit extends along a substantial portion of the surface of the tank, and defines a gradually enlarging opening. Essentially, the movement of the material within the tank at the upper end thereof will have a counter-clockwise direction, or from left to right; and thus, the opening incrementally enlarges toward the right which then facilitates the movement of material into the conduit 37. The washer 29 is provided with a sloping bottom wall equipped with a conduit 29a at the lowermost extremity thereof, through which heavy materials are removed from the washer, and with an outlet 2% at the upper end thereof through which foam, froth and lightweight particles are withdrawn from the washer.

The conduit discharges into a centrifuge head or closure manifold 39 that remains stationary as the centrifuge is rotated, and is sealingly related thereto in order that there be no seepage of material therebetween. The centrifuge has an inverted, generally frustoconical configuration, and is equipped at the lower end thereof with an outlet 40 through which the liquid and any clays or other colloidal suspensions therein are discharged. Adjacent the upper enlarged end of the centrifuge is a draw-off manifold 41 communicating with the interior thereof, through which heavy waste materials are discharged as, for example, rocks (that is, materials having a greater weight than the grain kernels being washed). This latter material is drawn off through a manifold 42 communicating with the centrifuge 38 intermediate the ends thereof and at a location below that of the manifold 41. It is apparent that the manifolds 4-1 and 42 communicate with the centrifuge along the peripheral surface thereof, and that a sealing relation must be defined therebetween to prevent the loss of materials through such connections.

The manifold 42 discharges the wet wheat or other granular material toward the upper surface of a downwardly inclined screen 43, the lower end of which terminates above a conveyor 44. Heated air is blown upwardly through the screen 43 as indicated by the arrowed lines 45. Disposed above the screen 43 is a suction hood 46 adapted to be connected through a conduit 47 with a suction fan (not shown). The volume and velocity of the heated air indicated by the arrows 45 is sufficient to float the grain, which it is desired to recover, above the surface of the screen whereby this floating mass of grain flows downwardly and onto the conveyor 44 which carries it to storage containers where it is held pending further processing. Materials heavier than the grain will not be 38 through a supported by the air curtain, and will fall downwardly through the screen 43 and to an appropriate waste receiver therefor. Similarly, waste materials which are lighter in weight than the grain will be carried upwardly by the air stream and into the suction hood 46. Consequently, only the clean grain kernels will be delivered to the conveyor 41.

It will be evident that conventional air heaters (not shown) may be provided for supplying the heated air bank flowing upwardly through the screen 43; and since the heated air flows through the grain mass and intimately surrounds the grain kernels throughout the entire path of movement thereof across the length of the screen, an eflicient drying of the grain is attained; and because the drying effect is directly related to the temperature of the air, it may be regulated by appropriate selection of the temperature thereof. Therefore, an accurate control over the moisture content of the grain delivered to the conveyor 44 is provided.

It will be apparent that the functioning of the apparatus described comprises a cleaning process wherein granular materials such as wheat, other grains, etc., are first mixed with a liquid such as water to thoroughly encase the particles in the liquid. Thereafter, the resultant mixture is agitated to effect a movement of the liquid over the surfaces of the solid particles to flush foreign materials therefrom. Certain of these foreign materials may be soluble in the liquid as, for example, smut removed by wash water from wheat kernels, and will thereafter remain in the liquid as a colloidal suspension. Other particles may not be soluble as, for example, small rocks or stones which are collected with the wheat, certain types of earth and dirt particles, etc. Though flushed from the granular material, such foreign solids will remain in the liquid and will be randomly distributed there-through along with the granules.

Next, the various solids in the water are stratified to separate the grain. Such stratification is accomplished in accordance with the weight, as by flotation in a centrifuge. It will be appreciated that numerous forces coact on the various particles to effect the stratification. First, there is the centrifugal force, and in view of the configuration of the centrifuge, the heavier particles such as rocks and stones will accumulate near the upper end of the centrifuge since the mass of such particles will result in a greater centrifugal force thereon for a given velocity of the centrifuge. As is well known, various other factors in addition to centrifugal force act on solids contained within a liquid disposed in a centrifuge, and for convenience some of the more important of these factors will be mentioned. Thus, because the particles are contained in a liquid body, the inherent buoyancy if any of such particles will tend to make them rise within the centrifuge because of the liquid pressure exerting an upward force on the particles. The greater the specific gravity of each of the particles, the less effective will be the net effect of the upward liquid pressure tending to cause the same to rise because the existing downwardly acting gravitational forces will have a greater net effect on such heavier particles. Also, the frictional force between certain of the particles and the surface of the centrifuge will have some incidental determination of the final position attained by the particles.

Considering all of these factors which are present in any centrifuge and selecting the proper centrifuge in accordance therewith, a stratification of the solids is accomplished and the grain along with other particulate matter of generally similar mass will comprise a stratum, which is then withdrawn from the centrifuge. These materials are again stratified in an air stream having a velocity such that particles heavier than the grain fall downwardly through the air stream and into a collection receptacle therefor. 'On the other hand, particles that are lighter than the grain are carried upwardly and are collected in the suction hood 46. The intermediate grain stratum is floated through the air stream and is deposited on a conveyor. Thus, the separation of the grain from the foreign materials comprehends a flotation or stratification thereof, both in liquid and gaseous media.

The air is heated to a temperature such that the grain which accumulates moisture in the mixing, washing and liquid flotation procedures, is dried to whatever moisture content is required. Ordinarily, the moisture content desired varies from about to depending upon the particular mill. To remove a greater amount of moisture from the grain, it is only necessary to elevate the temperature of the air stream, and such control over the air temperature is an easy procedure of considerable accuracy and may be determined manually or automatically. Consequently, the moisture content of the grain may be accurately controlled by means of this drying procedure.

In certain areas and in some installations, it may be feasible to eliminate the mixer 10 and pump 16; and in such event the wash water and wheat may be introduceod directly into the washer 29. Such a condition is illustrated in the drawing by the conduits 11' and 12.. The water will be fed into the washer through the conduit 11, and wheat solids through the conduit 12', and consequently a screw conveyor 13 is illlustrated in conjunction with the latter conduit. A direct introduction of the materials in the washer 29 is particularly suitable with the liquid stratification apparatus shown by broken lines at the right side of the drawing.

Such stratification apparatus can be used alternatively with the centrifuge 38 which, as has been brought out before, is simply a liquid stratification device. Thus, it may be used with the direct introduction of the water and grain into the washer, or with the prior described arrangement wherein the water and wheat solids are first mixed in the device 10, and are further mixed and agitated in the pump 16.

Where this apparatus is employed, the wheat and wash water will be removed from the washer 29 through the conduit 37 which empties into the stratification container 38. The admixture of wheat and wash water is preferably fed into the container 38' adjacent the upper end thereof, and it will be noted that this container is provided with a draw-01f pipe or outlet conduit 40' at its upper end, and with a screw conveyor 42' connecting therewith at its lower end. An air inlet 48 is connected to the inclined bottom wall of the tank or container 38, and has a screen 49 extending thereover. The screen will be a fine mesh member having countless tiny apertures that permit air and liquid to move therethrough, but which will prevent grain and particles of similar size from passing through it.

While the grain and water admixture is fed into the upper end portion of the tank, air is blown thereinto through the infeed conduit 48. The air stream is broken up by the fine mesh of the screen 49, and moves upwardly through the tank as a mass or blanket of bubbles. Such bubbles entrap the materials that are lighter than the grain particles, such as chafi, straw, dust, etc., and carries the same upwardly to the conduit 40' which removes this material from the tank. The heavier grain and any other heavier particles move downwardly through the tank 38, and the grain is withdrawn therefrom by means of the screw conveyor 42'. Particles and other matter which are heavier than the grain will descend to the lowermost portion of the tank 3 8', and may be withdrawn therefrom through a suitable outlet.

The conveyor 42 leads to the air Stratification apparatus heretofore described, and terminates at the same location as that of the conduit 42. Thus, the grain is dried by the heated air 45 and is further separated from both lighter and heavier particles as set forth hereinbefore, and is then deposited on the conveyor 44.

6 It has been found that the washing procedure may be facilitated by mixing a chemical additive with the wheat and wash water admixture. The function ()Psuch chemical additive is to assist in the separation of the grain? from the unwanted materials in the liquid separation or Stratification step. More specifically, the additive serves to increase the rate of precipitation and flotation. Consequently, an additive may be used which serves as a wetting agent to cut the of grease off of the wheat particles-that is, it reduces the surface tension of the water, thereby permitting the grain particles to become wet so that the buoyancy thereof is decreased and they sink or descend through the liquid body much more rapidly. Also, the light weight particles which are removed from the grain are encapsulated in a film provided by the additive, and are carried upwardly through the water at a more rapid rate. An example of such additive is pine oil.

Desirably, the chemical additive is employed with the liquid separation apparatus 38 for the rising air bubbles are encased in an oil film surface, and thereby trap the dirt and unwanted particles and more readily carry the same to the upper end of the tank for discharge therefrom through the conduit 40. The additive may be introduced into the wheat and water admixture at various locations in advance of the liquid separation or stratification equipment, as for example, just prior to the infeed of the mixture into the washer 29 as shown in the drawing.

While in the foregoing specification an embodiment of the invention has been set forth in considerable detail for purposes of presenting an adequate disclosure thereof, it will be apparent to those skilled in the art that numerous changes may be made in such details without departing from the principles and spirit of the invention.

I claim:

1. In a process for cleaning wheat and the like, the steps of mixing the wheat with water, agitating the resultant mixture in a washer to flush foreign materials from the wheat, isolating the wheat by flotation and stratification from both lighter weight and heavier weight solids in the mixture in accordance with the relative weights thereof, and withdrawing the wheat thus isolated from the washer.

2. The process of claim 1 in which the further step is included of isolating the withdrawn wheat from other of the solids withdrawn therewith by introducing the withdrawn material into a container and by passing air bubbles upwandly therethrough to effect an upward movement of the lighter weight solids while those of heavier weight precipitate downwardly through the bubbles.

3. The process of claim 2 in which theistep is included of introducing a wetting agent into the mixture prior to the aforesaid step of passing air bubbles therethrough.

References Cited in the file of this patent UNITED STATES PATENTS 417,273 Parkinson Dec. 17, 1889 509,728 Gillespie Nov. 28, 1893 583,082 Prinz May 25, 1897 1,201,934 Callow Oct. 17, 1916 2,442,522 Wiegand June 1, 1948 2,500,100 Strezynski Mar. 7, 1950 2,586,818 Harms Feb. 26, 1952 2,653,801 Fontein Sept. 29, 1953 2,743,817 Musgrave May 1, 1956 2,791,404 Kelly May 7, 1957 2,829,771 Dahlstrom Apr. 8, 1958 

1. IN A PROCESS FOR CLEANING WHEAT AND THE LIKE, THE STEPS OF MIXING THE WHEAT WITH WATER, AGITATING THE RESULTANT MIXTURE IN A WASHER TO FLUSH FOREIGN MATERIALS FROM THE WHEAT, ISOLATING THE WHEAT BY FLOTATION AND STRATIFICATION FROM BOTH LIGHTER WEIGHT AND HEAVIER WEIGHT SOLIDS IN THE MIXTURE IN ACCORDANCE WITH THE RELATIVE WEIGHTS THEREOF, AND WITHDRAWING THE WHEAT THUS ISOLATED FROM THE WASHER. 